Why do seahorses have square tails?

Dr. Michael Porter is an assistant professor of mechanical engineering at Clemson University. Here he explains how understanding the unique shape of seahorse tails could help scientists build better robots. Questions and answers have been edited.

Q: How is the seahorse tail different from other animals’ tails?

A: The tails of almost every animal – from cats to lizards, rats to monkeys – are round or cylindrically shaped. In contrast, the tail of a seahorse is square. It is made up of a series of overlapping segments arranged into square rings that are hitched together with flexible, pivoting joints like those found in our hips and shoulders.

Q: How did your lab figure out the advantages of a square tail? What’s so great about being square?

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A: A few years ago, we wondered what mechanical advantages could have helped to drive the evolution of the seahorse’s unusual appendage. To find out, we created a 3D-printed model that mimicked the square prism of a seahorse tail and a hypothetical version that was cylindrical. Then we abused the models, hitting them with a rubber mallet and twisting them and bending them to see how they responded. What we found was pretty amazing. The square structure of a seahorse tail is three times stiffer, four times stronger, and one and a half times more elastic than its circular counterpart when crushed.

Q: What potential uses do you foresee for a robotic seahorse tail?

A: This shape could lead to the development of new and improved robotic arms or manipulators for industry, military, or medicine. These robotics would be similar to many other tentacle- and snake-like robots, but the plated armor would allow the seahorse-inspired devices to be more lightweight and flexible than traditional hard robots and more robust and resistant to failure than soft robots. Potential applications include drill sheaths for gas and oil exploration, flexible body armors or motion-assist human exoskeletons for the military or disabled persons, and medical devices such as stents or catheters.

Q: You’ve said that nature is your experimental playground – how so?

A: The imitation of nature – a field known as biomimicry or bioinspired design -– has led to many real-world applications. For example, the invention of Velcro was inspired by burrs, the seed casings that catch onto clothing or animal fur. Nature provides researchers (particularly engineers) countless examples of working solutions to modern design challenges. However, nature's designs can be somewhat constrained, both by their environment and by evolution. So the “natural” solution may not always be the “best” solution. That is why new technologies, like 3D-printing, are useful. They allow us to mimic biological designs, but also build hypothetical models of designs not found in nature. We can then test them against each other to find inspiration for new engineering applications and also explain why biological systems could have evolved.